The present invention relates to a gas adsorber and, more particularly, to an adsorber which is suitable for use in processing systems that pretreat adsorptively waste gases containing mainly harmful gases, including those discharged from processes in the semiconductor industry, the ceramic industry, etc. to remove harmful components therefrom before the waste gases are released from the systems.
To pretreat harmful waste gases from semiconductor manufacturing processes and the like by an adsorption method, the following supervisory requirements must be satisfied: First, it is necessary to employ a means for accurately detecting the breakthrough point of the adsorbent used. Secondly, it is necessary to take measures to prevent harmful components from leaking out from the adsorber while the process is suspended until the adsorbent is replaced with a new one after the detection of the breakthrough point.
As an apparatus that satisfies these requirements to a certain extent, a treating apparatus has been proposed (Japanese Utility Model Public Disclosure (KOKAI) No. 62-123234) which comprises a main treating section including a main treating chamber having a large capacity and packed with a treating agent and an indicator that indicates the treating capacity of the main treating chamber, and a sub-treating chamber having a capacity which is about one tenth of that of the main treating chamber, the sub-treating chamber being connected in series to the main treating section at the downstream side thereof, so that waste gas flowing out from the main treating section is treated in the sub-treating chamber in supplementary manner.
However, the prior art cannot completely satisfy the above-described requirements in regard to the following points:
Although the change in color of the indicator is adopted as a means for detecting the breakthrough point of the adsorbent, which is the first requirement, the breakthrough of the adsorbent cannot be known before it occurs unless the indicator is constantly monitored, and it is impossible to know how long a harmful gas has flowed into the sub-treating chamber from the main treating chamber at the time when the operator becomes aware of a change in the color of the indicator and also impossible to know the concentration of the harmful gas. In consequence, the level of load on the post-stage sub-treating chamber cannot exactly be known, and there may be cases where the harmful gas leaks out from the sub-treating chamber, resulting in a failure to satisfy the second requirement. It is necessary in order to avoid such a problem to increase the size of the sub-treating chamber so that it has a sufficiently large treating capacity. However, such a solution merely results in an increase in the overall size of the apparatus and cannot satisfy the second requirement since it is still impossible to control the concentration of the gas flowing into the sub-treating chamber. In addition, the larger the surplus of the treating capacity of the sub-treating chamber, the larger the amount of adsorbent remaining unused in the sub-treating chamber when it is replaced, which is extremely uneconomical.
The detection method that utilizes a change in color of the indicator involves the problem that a coexisting component may cause the indicator to fade or shade after it has changed color, thus making it difficult to detect the breakthrough point. In such a case, the sub-treating chamber cannot serve to attain the original object.
Further, in the prior art the main treating section and the sub-treating chamber, which are provided separately from each other, are connected together through a valve so that waste gas can be supplied directly to the sub-treating chamber through a bypass while the adsorbent in the main treating chamber is being replaced. With such an arrangement, however, gas is constantly flowing into the sub-treating chamber, so that the adsorbent in the sub-treating chamber can be replaced only after the suspension of the operation of the factory. Nevertheless, it is impossible to know the amount of harmful gas which has already flowed into the sub-treating chamber, as described above. Therefore, the process may invite such a situation that the treating agent in the sub-treating chamber which should be replaced is used until the operation of the factory is suspended, resulting in an incomplete treatment. Moreover, when the waste gas that bypasses the main treating section is treated in the sub-treating chamber only, the sub-treating chamber must treat a harmful gas of high concentration for a time longer than a predetermined period, although it is usually only required to treat a relatively small amount of harmful gas leaking out from the main treating section. Therefore, if the flow rate of waste gas or the content of harmful components is excessively high, the sub-treating chamber, which has a treating capacity that is about one tenth of that of the main treating chamber, may fail to treat the waste gas completely.
Thus, the prior art lacks reliability in the means for detecting a breakthrough in the main treating section and cannot control the concentration of the waste gas leaking out from the main treating section after the detection of the breakthrough. Accordingly, the sub-treating chamber, which is additionally installed, cannot serve to attain the original object, and moreover, no consideration has been given to the method of controlling the sub-treating chamber, which is essential. In consequence, there is a probability of harmful components leaking out to the downstream side of the adsorber.